Method to accelerate torque transmitting conditions within a clutch

ABSTRACT

Within the scope of the method for acceleration of the torque breakdown of clutches in automatic transmissions, the follow-up of the hydraulic pressure and therewith the torque breakdown are accelerated by an over-compensation in the control.

[0001] According to the preamble of claim 1, the invention concerns a method for accelerating the torque breakdown of clutches in automatic transmissions.

[0002] Constantly increasing demands are being made at present on the functionality of automatic transmission: on one hand, more spontaneity is required, on the other hand, the clutches for different gear shifts are being repeatedly used to take into consideration the more compact design of the transmissions. Besides, the driver has a constantly increasing number of gears available to be shifted, the same as the possibility of manual engagement by the driver (tipp function). In addition, the driver must have the possibility of discontinuing or canceling gear shifts.

[0003] This results in the engagement and disengagement of the clutches is too slow or in engagement and disengagement at the right moment is becoming more and more difficult.

[0004] If, for example, a clutch is not filled enough and, nevertheless, has to become positively engaged at the next moment, this can lead to significant damage to the shifting quality. Conversely, considerable damages to shifting quality in automatic transmissions can result when a clutch takes up the torque too early or when the torque take-up lasts too long

[0005] According to the prior art, the above described problem is solved by the fact that prohibition times are introduced between the gear shifts. The effect of the prohibition times is that the clutch assumes a well-defined state such as “clutch full” or “clutch empty”.

[0006] Furthermore, discontinuation or the cancellation of gear shifts are prohibited or allowed only within a very limited scope. During torque build-up, the driving is usually at charge pressure whereby a torque take-up of long duration is produced by the follow-up control pressure.

[0007] Therefore, the problem on which this invention is based is to obtain as quickly as possible in a positively engaged clutch, a torque breakdown and therewith a spontaneous reaction to the rotational speed of the engine.

[0008] However, despite the quick torque breakdown, the clutch must remain at charge pressure in order to ensure the possibility of discontinuing or canceling gear shifts (immediate torque take-up).

[0009] This problem is solved by the features of claim 1. Other developments and variations result from the sub-claims.

[0010] Accordingly, It is proposed to accelerate the follow-up of the hydraulic pressure and thus the torque breakdown by an over-compensation of the control in a positively engaged clutch.

[0011] According to the invention, this is achieved by driving the pressure control below the charge pressure level. The torque breakdown is accordingly carried out quickly due to the increased pressure difference.

[0012] After a certain applicable time over an applicable pressure ramp, it is then returned again to filler pressure in order, by the pressure difference, to ensure or produce the immediate torque take-up again.

[0013] For the case that a change of shifting condition or a discontinuation of the shifting operation is carried out, or when the gear shift is canceled, the control abandons the controlled opening pressure. According to the invention, in this case an applicable pressure pulse is controlled in order, by the increased pressure difference, immediately to set the clutch again at charge pressure level so that the torque take-up be ensured. This can also occur by take-up of the time-dependent rapid filling.

[0014] The method is described, in detail below, with reference to the enclosed FIGURE. In this FIGURE the pressure progress during torque breakdown is shown as function of time according to the prior art and according to the instant invention.

[0015] In the FIGURE, according to the prior art, during torque build-up the driving is at charge pressure (curve 1) by means of the electric control whereby is produced by the follow-up control pressure a long-lasting torque take-up. Curve 2 in the FIGURE corresponds to the progress in time of the follow-up control pressure. At the moment B, the torque breakdown terminates and the clutch is ready for torque take-up.

[0016] Contrary to the prior art, within the scope of the inventive method during the electric control, the charge pressure P_Full has fallen below by Δ_P1 with the result that the curve 3 of the follow-up control pressure drops more abruptly whereby the torque breakdown is carried out more quickly due to the increased pressure difference. The torque breakdown terminates at the point B1: it can be seen from the FIGURE, the torque breakdown operation is considerably accelerated by Δ_t.

[0017] The readiness to immediate torque take-up is ensured by the fact that after a certain applicable time t_start_ramp, which can be as long as desired, the charge pressure P_Full is adjusted via a likewise applicable pressure ramp (curve 4 in the FIGURE). This moment is designated C1 in the FIGURE. The time t_start ramp depends on the actual attainment of the charge pressure P_Full via the hydraulics.

[0018] In the FIGURE is also outlined the case that a change of shifting state or a discontinuation of the shifting operation prior to expiration of the time t_start ramp is carried out. As already explained in this case, an applicable pressure pulse 5 is controlled so that the charge pressure is exceeded by Δ_P2 (point D). The adjustment of the charge pressure level is accelerated by the increased pressure difference so that the torque take-up at the moment C2 is ensured.

[0019] The method shown here is adequate for all clutches which have a hydraulic pressure follow-up to the electric control.

[0020] One other advantage of the invention is the increase in spontaneity achieved thereby both at low and at high temperatures. 

1. Method for accelerating the torque breakdown of clutches in automatic transmissions which are electrically controlled and have a hydraulic pressure follow-up, characterized in that the follow-up of the hydraulic pressure and therewith the torque breakdown are accelerated by an overcompensation in the control.
 2. Method according to claim 1, characterized in that when opening the clutch, the pressure control is driven by a pressure difference (Δ_P1) below a pressure level of a charge pressure (P_Full) in a manner such that the torque breakdown is accelerated.
 3. Method according to claim 2, characterized in that following a certain arbitrarily long applicable time (t_start_ramp), the charge pressure (P_Full) is adjusted via an applicable pressure ramp (4) to ensure, or produce again, the immediate torque breakdown.
 4. Method according to any one of the preceding claims, characterized in that for the case that a change of shifting state or a discontinuation of the shifting operation is carried out prior to expiration of the applicable time (t_start_ramp), or when the gear shift is canceled, an applicable pressure pulse (5) is controlled in a manner such that the pressure level of the charge pressure (P_Full) is exceeded by a pressure difference (Δ_P2) in order, by increased pressure, immediately to set the clutch again at the actual pressure level of the charge pressure (P_Full) so that the torque take-up be ensured. 